Camshaft drive system for internal combustion engine

ABSTRACT

A camshaft drive system for an internal combustion engine includes a drive sprocket fixed upon a crankshaft of the engine and a driven sprocket fixed upon a camshaft of the engine. A flexible power transmission element extends between the drive sprocket and driven sprocket. A tensioning device for the flexible power transmission element includes a linear actuator and a number of movable contactors for engaging and tensioning both the slack side and the tight side of the power transmission element, such that proper phasing of the camshaft with respect to the crankshaft is maintained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a mechanism for powering a cylinderpoppet valve operating camshaft of an internal combustion engine with aflexible power transmission member driven by the engine's crankshaft.

2. Disclosure Information

Internal combustion engine camshafts have typically been driven eitherby a gear train, as in heavy duty engines, such as certain dieselengines, or by flexible transmission members such as chains or belts,typically used in gasoline engines and medium duty diesel engines. Geardrives provide the most precise control over the position of thecamshaft throughout the engine's useful life. However, gear drives areexpensive and generate much more noise than chain or belt drives. On theother hand, although chain and belt drives are less expensive than geardrives, the inevitable wear of chains and belts has caused problems athigh mileage with certain engines because mispositioning of thecamshaft, as will occur where a tensioner for the chain or belt isapplied at only one side of the chain or belt, typically the slack side,will cause phasing of the camshaft with respect to the engine'scrankshaft to be changed as the chain or belt wears. This is undesirablefor reasons of performance, emissions, fuel economy, and sometimes and,ultimately, engine life in the case of certain engines, wherein a lackof free-wheeling construction means that excessive loss of phase controlof the camshaft results in catastrophic destruction of the enginebecause the pistons of the engine contact the valves at top dead center.

A camshaft drive system according to the present invention providesaccurate control of the camshaft phasing, in the context of a lessexpensive belt or chain system, using hardware which is available at areasonable cost.

SUMMARY OF THE INVENTION

A camshaft drive system for an internal combustion engine includes adrive sprocket fixed upon a crankshaft of the engine, and a drivensprocket fixed upon a camshaft of the engine. A flexible powertransmission element extends between the drive sprocket and the drivensprocket. The flexible power transmission element has a slack side and atight side. A tensioning device includes a linear actuator having anaxis of operation which is parallel to a line extending from the centerof the drive sprocket to the center of the driven sprocket. A number ofmovable contactors for engaging, and thereby tensioning, the slack sideand the tight side of the flexible power transmission element areoperably connected with, and movable by, the linear actuator such thatmovement of the linear actuator in a selected direction along its axisof operation will cause the slack side and the tight side of theflexible power transmission element to be displaced, and therebytightened, equally.

A linear actuator useful for incorporation in the present systempreferably includes a spring-loaded plunger which is mounted within acylinder furnished with a supply of oil under pressure from an enginelubrication system such that force exerted by the spring and the oilupon the plunger combine to urge the contactors, which may be eitherrollers or guide shoes, in a direction tending to tighten the flexiblepower transmission element equally on both the tight and slack sides.

According to another aspect of the present invention, the presentcamshaft drive system may further include a number of stationarycontactors rigidly mounted adjacent to the flexible power transmissionelement, whether it be a chain or a belt, with at least one of thestationary contactors bearing upon the slack side of the powertransmission and another one of the stationary contactors bearing uponthe tight side of the power transmission element, such that the travelof the movable contactors needed to remove slack from the powertransmission element is reduced.

According to another aspect of the present invention, a movablecontactor incorporated in the present camshaft drive system may be movedeither slidingly in the same direction of movement as the direction ofmovement of the linear actuator, or, alternatively, the contactors maybe moved laterally inward in response to movement of the linearactuator. As yet another alternative, the movable contactors may berotated in response to movement of the linear actuator.

It is an advantage of a camshaft drive system according to the presentinvention that precise control of the camshaft phasing is maintainedthroughout the useful life of an engine.

It is another advantage of a camshaft drive system according to thepresent invention that the present system is quieter than known geardrive systems.

It is yet another advantage of the present camshaft drive system thatthe present system may be employed at less cost than known camshaftdrive systems achieving accurate control of camshaft phasing.

Other advantages, as well as features and objects of the presentinvention, will become apparent to the reader of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an engine having a camshaft drive systemaccording to the present invention.

FIG. 2 is an embodiment of the present invention having slidable guideshoes for tensioning a power transmission element.

FIG. 3 is similar to FIG. 2, but shows a system having guide shoes whichare pivoted.

FIG. 4 is similar to FIGS. 2 and 3, but illustrates a system havingguide shoes which are displaceable laterally.

FIG. 5 is similar to FIG. 4, but shows a system according to the presentinvention having rotatable rollers employed as contactors for engagingand tensioning a flexible power transmission element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, engine 10 has crankshaft 18 with a drive sprocket,14, attached thereto. Camshaft 26, having a camshaft sprocket, 22,attached thereto, is driven by means of flexible power transmissionelement 30, which has a tight side 31 and a slack side 34. Those skilledin the art will appreciate in view of this disclosure that flexiblepower transmission element 30 could comprise either a metallic linkchain, or a metallic or non-metallic belt. The choice of a particulartype of flexible power transmission element for use with the presentinvention is committed to those wishing to practice this invention.

FIG. 1 also shows two contactors, 32, which are depicted as two rollers.Those skilled in the art will further appreciate that contactors 32could be smooth or toothed, and this is true regardless of whetherflexible power transmission element 30 comprises either a chain or abelt.

Contactors 32 are attached to a movable bridge 44, which has a slider 48fitted into channel 52 formed in plate 56, which is attached to an endportion of engine 10. Movable bridge 44, as well as contactors 32, ispositioned by means of linear activator 60, which includes a plunger,68, mounted for reciprocation within a cylinder, 64. Spring 72 ispositioned within cylinder 64 so as to bias linear actuator 60, as wellas movable bridge 44 and contactors 32, in a direction away fromcrankshaft 18 and towards camshaft 26. Thus it is seen that linearactuator 60 has an axis of operation which is parallel to a lineextending from center of drive sprocket 14 to the center of cam sprocket22. Further, in the embodiment of FIG. 1, linear actuator 60 has an axisof operation which is coincident with a line drawn between the centerline of crankshaft 18 and the center line of camshaft 26.

The interior of cylinder 64 is filled with engine oil which is furnishedunder pressure from an engine lubrication system (not shown) throughvalve 82 and line 78. The oil forces plunger 68 upwards, so as totension power transmission element 30. Stated another way, linearactuator 60 exerts a force which is in a direction tending to tightenflexible power transmission element 30 by pushing movable bridge 44 inthe direction of camshaft 26 and cam sprocket 22. Because bridge 44 ismounted to plate 56 by means of slider 48 and channel 52, contactors 32displace tight side 31 and slack side 34 of power transmission element30 equally, preventing any camshaft phase change from occurring.

Force exerted by linear actuator 60 is equal to the sum of the springforce provided by spring 72 and hydraulic force exerted by lubricatingoil upon plunger 68. Because check valve 82 is positioned in line 78,linear actuator 60 is prevented from retracting in response to theforces imposed by power transmission element 30 upon contactors 32.Those skilled in the art will appreciate in view of this disclosure thatother types of linear actuators could be incorporated in the presentcamshaft drive system.

FIG. 1 also shows a fixed bridge 40, having two additional fixedcontactors, 36, applied thereto. Bridge 40 and contactors 36 serve tobear upon tight side 31 and slack side 34 equally such that the travelof movable contactors 32 required to remove slack from both sides ofpower transmission element 30 is reduced.

FIG. 2 illustrates a second embodiment in which bridge 90 has two guideshoes 86 attached thereto which are, once again, slidingly engaged withpower transmission element 30 so as to tension both sides of powertransmission element 30 without changing phasing between camshaft 26 andcrankshaft 18. In essence, guide shoes 86 are sliders which guide powertransmission element 30 without the need for the rotation present withcontactors 32 illustrated in FIG. 1. As with the previous embodiment,linear actuator 60 provides the force required to tension powertransmission element 30. Guide shoes 86 may be constructed of metallic,non-metallic, or composite materials known to those skilled in the artand suggested by this disclosure.

FIG. 3 illustrates an additional embodiment in which guide shoes 94 arepivoted upon pivots 98 to front plate 56. In the embodiment shown inFIG. 3, guide shoes 94 are biased inwardly by the action of bridge 106and guide pins 102, which are acted upon by linear actuator 60.

In FIG. 4, guide shoes 108 have cutouts 110 which are engaged by contactpads 120, which are attached at the ends of fingers 112, which arepivoted upon pivots 116 such that linear actuator 60 causes guide shoes108 to move laterally together by an equal amount to properly tensionpower transmission element 30 in response to movement of the linearactuator.

FIG. 5 illustrates an embodiment which uses rollers 122, which areattached to fingers 126 pivoted upon pivots 130, with fingers 126 beingrotated as before, by means of linear actuator 60. Eccentric lock 134 isprovided to bear on an extension of one of fingers 126 so as to preventback-driving of finger 126b in response to the forces acting upon tightside 31 of power transmission element 30.

While particular embodiments of the invention have been shown anddescribed, numerous variations and alternate embodiments will occur tothose skilled in the art. Accordingly, it is intended that the inventionbe limited only in terms of the appended claims.

1. A camshaft drive system for an internal combustion engine,comprising: a drive sprocket fixed upon a crankshaft of said engine; adriven sprocket fixed upon a camshaft of said engine; a flexible powertransmission element extending between said drive sprocket and saiddriven sprocket, with said power transmission element having a slackside and a tight side; and a tensioning device for said flexible powertransmission element, with said tensioning device comprising: a singlelinear actuator having an axis of operation which is parallel to a lineextending from the center of said drive sprocket to the center of saiddriven sprocket; a plurality of movable contactors for engaging andthereby tensioning said slack side and said tight side of said flexiblepower transmission element, with each of said plurality of contactorsbeing connected with, a single bridge, slidingly movable by said singlelinear actuator in the direction of movement of said single linearactuator such that movement of said single bridge and said single linearactuator in a selected direction along said axis of operation will causesaid slack side and said tight side of said flexible power transmissionelement to be displaced equally; and a plurality of stationarycontactors rigidly mounted adjacent to said flexible power transmissionelement, with at least one of said stationary contactors bearing uponsaid slack side of said power transmission element, and at least anotherone of said stationary contactors bearing upon said tight side of saidpower transmission element, such that the travel of said plurality ofmovable contactors needed to remove slack from said power transmissionelement is reduced.
 2. A camshaft drive system according to claim 1,wherein said linear actuator comprises a spring-loaded plunger.
 3. Acamshaft drive system according to claim 1, wherein said linear actuatorcomprises a spring-loaded plunger slidably mounted within a cylinderfurnished with a supply of oil under pressure from an engine lubricationsystem, such that the force exerted by said spring and said oil uponsaid plunger combine to urge said contactors in a direction tending totighten said flexible power transmission element.
 4. A camshaft drivesystem according to claim 3, wherein said oil is admitted into saidcylinder through a check valve which prevents oil from leaving saidcylinder.
 5. A camshaft drive system according to claim 1, wherein saidflexible power transmission element comprises a metallic chain.
 6. Acamshaft drive system according to claim 1, wherein said flexible powertransmission element comprises a nonmetallic belt.